The present invention relates to a method and apparatus for obtaining an image; and more particularly, to a method and apparatus for obtaining a high-resolution image of a controllable rotating target by using an image reconstruction algorithm without interpolation.
Conventional imaging techniques including ISAR (Inverse Synthetic Aperture Radar), CT (Computerized Tomography) and MRI (Magnetic Resonance Imaging), for a controllable rotating target, have been used in various application areas, e.g., modeling and analysis of targets. Also, they have been adopted as a diagnostic method to support the medical and physical sciences and used to develop the target detection, recognition and classification techniques.
Referring to FIG. 1, there is shown a conventional imaging apparatus for obtaining a high resolution image of a rotating target, wherein the targets are linearly rotated. As shown in FIG. 1, the conventional imaging apparatus 100 generally samples a reflected signal from a target 180 on the polar coordinates of frequency and observation angle. The conventional imaging apparatus 100 comprises a rotating stage 110, a driving unit 120, a transmitting antenna 130, a receiving antenna 140, a reference signal generation unit 150, a controlling and signal processing unit 160 and a display unit 170.
The target 180 is mounted on the rotating stage 110. The driving unit 120 includes, e.g., a motor for rotating the rotating stage 110 and is physically connected to the rotating stage 110. Also, the driving unit 120 is electrically connected to the controlling and signal processing unit 160. The transmitting antenna 130 is electrically coupled to the controlling and signal processing unit 160 via the reference signal generation unit 150. The transmitting antenna 130 transmits to the target 180 a reference signal from the reference signal generation unit 150, whereas the receiving antenna 140 receives a reflected signal from the target 180 to transfer it to the controlling and signal processing unit 160. The controlling and signal processing unit 160 processes the reflected signal transferred from the receiving antenna 140 to provide a 2-dimensional image for the target 180. In this processing, the controlling and signal processing unit 160 applies the conventional 2-dimensional image reconstruction algorithm including interpolation to the reflected signal containing measured data for the target 180, thereby providing a 2-dimensional image.
For a small observation angle, a high-resolution image can be achieved in a short processing time by using an unfocused reconstruction algorithm because the received data can be modeled by samples of the Fourier transform on rectangular coordinates. But, if the observation angle range is not very small, the unfocused image is degraded by the blur effect. The blur effect can be removed by the reformatting of received data on rectangular lattice by using the interpolation in the focused image. However, the additional interpolation process leads to a longer processing time than the unfocused algorithm and the image degradation due to artifacts.
It is, therefore, an object of the present invention to provide a method and apparatus for obtaining a high-resolution image of a controllable rotating target by using an image reconstruction algorithm without interpolation.
In accordance with one aspect of the present invention, there is provided an imaging method capable of obtaining 2-dimensional high-resolution image of a controllable rotating target during a short image processing time without degrading the quality of the image, wherein the imaging method is employed in an imaging apparatus comprising means for controlling the imaging apparatus and processing a signal reflected from the target, means for generating a reference signal, means for transmitting and receiving the reference signal and means for rotating the target, the method comprising the steps of: a) acquiring initial information concerning the imaging apparatus and the target; b) calculating parameters for use in rotating the target, the parameters including a rotational increment of the rotating means and a total rotation angle thereof; c) computing a start frequency ƒsk and a step frequency xcex4ƒk; d) measuring data for the target to store them based on the values obtained in the steps a) to c); e) determining whether or not the step d) is completed; f) if the determination result is negative, repeating the steps a) to e); and, if otherwise, obtaining the 2-dimensional high-resolution image by using an image reconstruction algorithm; and g) displaying the 2-dimensional high-resolution image, wherein the image reconstruction algorithm applies a Fast Fourier transform (FFT) process to the measured data to reconstruct the 2-dimesional high-resolution image without interpolation.
In accordance with another aspect of the invention, there is provided an apparatus for obtaining a 2-dimensional high-resolution image by rotating a controllable target and measuring data for the controllable target at each of rotating angles, comprising: means for rotating the controllable target to a predetermined angle, wherein intervals between the predetermined angles are not identical to each other; means for generating a first signal; means for transferring the first signal to the controllable target; means for receiving a second signal reflected from the controllable target; means for converting the first and the second signal into a third and fourth signal, respectively, wherein the frequency of the third signal is different from that of the forth signal; and means for processing the third and forth signal to reconstruct an image representing the controllable target, and for controlling the rotating means, wherein the controlling and signal processing means applies a FFT (Fast Fourier Transform) algorithm to the measured data without interpolation.